Heat-assisted pumping systems for use in negative pressure wound therapy

ABSTRACT

A device and method for treating a wound of a patient with negative pressure is provided. The device comprises a heat-assisted pump system. The pump system can be powered in part by heat derived from the patient. The pump system may be configured to be highly planar, light weight, and portable. The pump system may comprise a Stirling engine or a thermal acoustic engine.

BACKGROUND OF THE INVENTION Field

This application is directed to systems and methods for treating a woundwith topical negative pressure (TNP) therapy. Embodiments disclosedrelate to pump systems and wound dressings for use in TNP therapy.

Background

Many different types of wound dressings are known for aiding the healingprocess of a human or animal wound. These different types of wounddressings include many different types of materials and layers, forexample, gauze pads, foam pads, absorbent layers, breathable layers,adhesive layers and non-adhesive layers.

Topical negative pressure (“TNP”) therapy, sometimes referred to asvacuum assisted closure, negative pressure wound therapy, or reducedpressure wound therapy, is widely recognized as a beneficial mechanismfor improving the healing rate of a wound. Such therapy is applicable toa broad range of wounds such as incisional wounds, open wounds andabdominal wounds or the like. TNP therapy assists in the closure andhealing of wounds by reducing tissue edema; encouraging blood flow;stimulating the formation of granulation tissue; removing excessexudates, and may reduce bacterial load and thus reduce the potentialfor infection of the wound. TNP therapy systems can also assist in thehealing of surgically closed wounds by removing fluid and by helping tostabilize the tissue in the apposed position of closure. A furtherbeneficial use of TNP therapy can be found in grafts and flaps whereremoval of excess fluid is important and close proximity of the graft totissue is required in order to ensure tissue viability. TNP therapypermits less outside disturbance of the wound and promotes more rapidhealing.

SUMMARY

Embodiments of the present disclosure relate to apparatuses and methodsfor wound treatment. Some of the wound treatment apparatuses describedherein comprise a pump system for providing negative pressure to a woundsite. Wound treatment apparatuses may also comprise wound dressings thatmay be used in combination with the pump systems described herein, andconnectors for connecting the wound dressings to the pump systems.

In accordance with one embodiment, a pump system is provided. The pumpsystem comprises a first member and a second member, the first memberhaving a higher temperature than the second member. The pump systemutilizes the heat differential between the first and second members todrive or assist the pump system in generating a vacuum pressure, therebyextending the portability and operational duration of the pump system.

In one aspect of the invention, the pump system comprises a Stirlingengine with a generally planar configuration. The Stirling enginecomprises a canted swash plate disposed between a hot plate and a coldplate.

Optionally, a vacuum pressure is generated by the compression of one ormore bellows by the movement of the swash plate.

In one aspect of the invention, the pump system comprises a thermalacoustic engine. The thermal acoustic engine is configured to transformthe sound wave generated by the thermal acoustic engine into a vacuumpressure that can be applied to the wound.

Optionally, the thermal acoustic engine comprises a diaphragm configuredto move in response to the sound wave generated by the thermal acousticengine.

Optionally, the pump system comprises a canister to receive the woundexudate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic perspective view of a pump system comprising aStirling engine.

FIG. 2 is a schematic cross-sectional side view of a pump systemcomprising a thermoacoustic engine.

FIG. 3A is a schematic top view of a wound dressing having a pump systemthat can be located away from the wound site.

FIG. 3B is a schematic top view of a wound dressing having a pump systemincorporated into the wound dressing.

FIG. 4A illustrates a step of preparing the skin near a wound site toreceive a wound dressing.

FIG. 4B illustrates a step of positioning a wound dressing over a wound.

FIG. 4C illustrates a step of securing a wound dressing over a wound.

DETAILED DESCRIPTION

It will be understood that embodiments of the present disclosure aregenerally applicable for use in TNP therapy systems. Briefly, negativepressure wound therapy assists in the closure and healing of many formsof “hard to heal” wounds by applying a negative pressure to the woundsite. Embodiments disclosed herein relate to apparatuses and methods oftreating a wound with reduced pressure, including pump and wounddressing components and apparatuses. The apparatuses and componentscomprising the wound overlay and packing materials, if any, aresometimes collectively referred to herein as dressings.

Many wound dressings used in TNP therapy employ a pump system togenerate a negative pressure at the wound site. Bulky or heavy pumpsystems compromise the portability of a TNP wound therapy system. On theother hand, small or light-weight pumping systems may have a limitedability to operate for a significant amount of time or may have alimited ability to deliver substantial negative pressures to the woundsite. One challenge associated with designing wound dressings for use inTNP therapy is achieving a portable dressing that can supply adequatenegative pressure to the wound for a substantial amount of time. Adevice that can be mounted on a dressing has not yet been devised thatcan operate for a commercially suitable length of time. Devices under 50cubic centimeters usually have upper operational durations of under twoweeks. Devices with 60-day operation capability may be bulky or requirerecharging.

The novel systems disclosed herein enable portable wound dressings forTNP wound therapy. Many of the disclosed embodiments provide pumpingsystems that have a long operational duration and are suitable for usein TNP wound therapy. In some embodiments, energy derived from thepatient is used, at least in part, to assist or drive the pumping systemthat generates the negative pressure at the wound site. In someembodiments, the pump system can be included as part of a woundtreatment apparatus which can include, for example, a wound dressing.Although not required, embodiments of the wound dressings hereindisclosed can be sterile.

In some embodiments, the pump system can be separate from the wounddressing as a standalone unit. This can beneficially allow the pumpsystem to be positioned at a different location away from the wounddressing. In some embodiments, the pump system can be attached to (e.g.,incorporated in) the wound dressing to form a single unit. This canpotentially reduce the form factor of the wound treatment apparatus andreduce the length of a conduit attaching the pump system to the wounddressing.

In some embodiments, the pump system can operate in a canisterlesssystem, in which the wound dressing retains exudate aspirated from thewound. Such a dressing can include a filter, such as a hydrophobicfilter, that prevents passage of liquids downstream of the dressing(toward the pump system). In other embodiments, the pump system canoperate in a system having a canister for storing at least part ofexudate aspirated from the wound. Such canister can include a filter,such as a hydrophobic filter, that prevents passage of liquidsdownstream of the dressing (toward the pump system). In yet otherembodiments, both the dressing and the canister can include filters thatprevent passage of liquids downstream of the dressing and the canister.

It will be appreciated that throughout this specification reference ismade to a wound. It is to be understood that the term wound is to bebroadly construed and encompasses open and closed wounds in which skinis torn, cut or punctured or where trauma causes a contusion, or anyother surficial or other conditions or imperfections on the skin of apatient or otherwise that benefit from reduced pressure treatment. Awound is thus broadly defined as any damaged region of tissue wherefluid may or may not be produced. Examples of such wounds include, butare not limited to, acute wounds, chronic wounds, surgical incisions andother incisions, subacute and dehisced wounds, traumatic wounds, flapsand skin grafts, lacerations, abrasions, contusions, burns, diabeticulcers, pressure ulcers, stoma, surgical wounds, trauma and venousulcers or the like. In some embodiments disclosed herein, the componentsof the TNP system described herein can be particularly suited forincisional wounds that exude a small amount of wound exudate.

As is used herein, reduced or negative pressure levels, such as −X mmHg,represent pressure levels that are below standard atmospheric pressure,which corresponds to 760 mmHg (or 1 atm, 29.93 inHg, 101.325 kPa, 14.696psi, etc.). Accordingly, a negative pressure value of −X mmHg reflectsabsolute pressure that is X mmHg below 760 mmHg or, in other words, anabsolute pressure of (760−X) mmHg In addition, negative pressure that is“less” or “smaller” than X mmHg corresponds to pressure that is closerto atmospheric pressure (e.g., −40 mmHg is less than −60 mmHg). Negativepressure that is “more” or “greater” than −X mmHg corresponds topressure that is further from atmospheric pressure (e.g., −80 mmHg ismore than −60 mmHg).

The operating negative pressure range for some embodiments of thepresent disclosure can be between approximately −10 mmHg to −200 mmHg,between −20 mmHg to −150 mmHg, between −45 mmHg to −100 mmHg, anysubrange within these ranges, or any other range as desired.

The pump system embodiments described herein can have a compact, smallsize. The diameter of the Stirling engine pump herein disclosed can bebetween approximately 5 mm to 400 mm, between 10 mm to 200 mm, between20 mm to 100 mm, any subrange within these ranges, or any other rangedesired. The thickness of the Stirling engine pump herein disclosed canbe between approximately 1 mm to 30 mm, between 2 mm to 20 mm, between 3mm to 10 mm, any subrange within these ranges, or any other rangedesired. The thermoacoustic path lengths for the pump systems hereindisclosed can be between approximately 1 mm to 150 mm, between 2 mm to100 mm, between 3 mm to 50 mm, any subrange within these ranges, or anyother range desired. By way of a non-limiting example, thethermoacoustic path length can range from 3.3 mm for a quarter waveoscillator to run at 26 kHz up to around 50 mm.

In some embodiments, the pump system uses a Stirling engine to drive orassist a pumping system that generates a negative pressure at the woundsite. Stirling engines are a method of harnessing energy from a hot heatexchanger. Generally, Stirling engines use cyclic compression andexpansion of an enclosed fluid (often called “the working fluid”) todrive the displacement of a piston. Because the working fluid isenclosed, Stirling engines may be powered by a variety of hot heatexchangers.

A Stirling engine includes generally includes two volumes that arefluidically connected to one another. One of the volumes containsworking fluid that is at a high temperature, while the working fluid inthe other volume is kept at a low temperature. A cycle of a Stirlingengine comprises two phases, herein referred to as (1) a power strokeand (2) a compression phase. During the power stroke phase, the workingfluid in the hot volume pushes against a drive piston, causing the drivepiston to move in the direction of the applied force. Mechanical work(which is the product of a force and a displacement in the direction ofthe force) is done during the power stroke of the Stirling engine cycle.During the compression phase, the drive piston is moved back to compressthe working fluid in the hot volume, thereby reseting the drive pistonfor another cycle of the engine.

Stirling engines have been designed in several configurations (e.g.,alpha, beta). Stirling engines often use a rotational crank as eitherthe output drive or as an intermediate state. Additionally, Stirlingengines tend to have a tall form factor when the crank mechanism isincluded. For incorporating into a wound dressing, Stirling engineshaving a planar configuration may be beneficial.

FIG. 1 depicts one embodiment of a pump system 100 that can include aStirling engine. The pump system 100 may be used for TNP therapy. Insome embodiments the pump system 100 can be incorporated into a portablewound dressing. In many embodiments, the pump system 100 can be planarand suitable for use in TNP therapy wound dressing.

In some embodiments, the pump system 100 can have a hot plate 102thermally connected to a hot heat exchanger. A cold plate 104 can bethermally connected to a cold heat exchanger and separated from the hotplate 102 by a distance. In some embodiments, the hot plate 102 canreceive at least a portion of its heat from the patient (e.g., the hotplate 102 can be in direct or indirect contact with the patient).

A swash plate 106 can be disposed between the hot plate 102 and the coldplate 104. In some embodiments, the swash plate 106 can be canted sothat a portion of the swash plate 106 is closer to the cold plate 104than to the hot plate 102 while a different portion of the swash plate106 is closer to the hot plate 102 than to the cold plate 104. In atleast one embodiment, the swash plate 106 can pivot about its center 107so that the point of the swash plate 106 that is closest to the hotplate 102 moves continuously around the circumference of the hot plate102.

The hot plate 102 can have a hot cylinder 110 that is thermally coupledto the hot plate 102. Similarly, the cold plate 104 can have a coldcylinder 112 that is thermally coupled to the cold plate 104. The hotcylinder 110 and the cold cylinder 112 can be fluidically connected toone another by a connecting line 114.

A working fluid 116 can be contained within the closed system formed bythe hot cylinder 110, the cold cylinder 112, and the connecting line114. In some embodiments, the hot cylinder 110 can be bounded on oneside by the hot plate 102 and on an opposing side by a drive piston 120.In some embodiments, the drive piston 120 can include a portion of theswash plate 106. In some embodiments, the drive piston 120 can becoupled to the swash plate 106 by an intermediate linkage (not shown).In some embodiments, the drive piston 120 can move within the hotcylinder 110. In some embodiments, the hot cylinder 110 can be aflexible bladder (e.g., bellows) that is sandwiched between the swashplate 106 and the hot plate 102.

The cold cylinder 112 can be bounded on one side by the cold plate 104and on an opposing side by a cold piston 122. In some embodiments, thecold piston 122 can include a portion of the swash plate 106. In someembodiments, the cold piston 122 can be coupled to the swash plate 106by a linkage (not shown). In some embodiments, the cold piston 122 canmove within the cold cylinder 112. In some embodiments, the coldcylinder 112 can be a flexible bladder (e.g., bellows) that issandwiched between the swash plate 106 and the cold plate 104.

In some embodiments, at the beginning of the power stroke phase, thedrive piston 120 can compress the working fluid 116 within the hotcylinder 110, driving some of the working fluid 116 through theconnecting line 114 and into the cold cylinder 112. As heat is added tothe hot cylinder 110 through the hot plate 102, the working fluid 116within the hot cylinder 110 can expand. The expansion of the workingfluid 116 can force the drive piston 120 away from the hot plate 102,causing the swash plate 106 to pivot. In some embodiments, the movementof the drive piston 120 away from the hot plate 102 can draw some of theworking fluid 116 from the cold cylinder 112, through the connectingline 114 and into the hot cylinder 110. In some embodiments, movement ofthe drive piston 120 can cause the swash plate 106 to compress the coldcylinder 112, causing some of the working fluid 116 in the cold cylinder112 to flow through the connecting line 114 and into the hot cylinder110. In at least one embodiment, the flow of the working fluid 116 fromthe cold cylinder 112 into the hot cylinder 110 can be the result ofboth the movement of the drive piston 120 drawing in the working fluid116 and the movement of the swash plate 106 squeezing the working fluid116 out of the cold cylinder 112.

The working fluid 116 in the cold cylinder 112 can be at a lowertemperature than the working fluid 116 within the hot cylinder 110. Atthe beginning of the compression phase of the engine cycle, the infusionof the working fluid 116 from the cold cylinder 112 into the hotcylinder 110 can reduce the temperature of the working fluid 116 withinthe hot cylinder. At the end of the power stroke phase, the swash plate106 can continue to move due to the momentum imparted to the swash plate106 by the drive piston 120 during the power stroke phase of the cycle.In some embodiments, the momentum imparted to the swash plate 106 cancause the swash plate 106 to pivot in a rolling fashion. In someembodiments, the momentum imparted to the swash plate 106 can cause theswash plate 106 to tilt back and forth.

As the swash plate 106 moves, the swash plate 106 can return the drivepiston 120 toward the hot plate 102. In some embodiments, the swashplate 106 can be configured so that movement of the swash plate 106draws the cold piston 122 away from the cold plate 104, causing theworking fluid 116 to be drawn from the hot cylinder 110, through theconnecting line 114, and into the cold cylinder 112. In at least oneembodiment, the flow of the working fluid 116 from the hot cylinder 110into the cold cylinder 112 can be the result of both the movement of theswash plate 106 drawing the working fluid 116 into the cold cylinder 112and the movement of the swash plate 106 squeezing the working fluid 116out of the hot cylinder 110.

The mixing of colder working fluid 116 from the cold cylinder 112 withhotter working fluid 116 in the hot cylinder 110 can reduce thetemperature of the working fluid 116 within the hot cylinder 110. Thepressure of a given volume of gas is inversely related to thetemperature of the gas. Accordingly, cooling the working fluid 116within the hot cylinder 110 before beginning the compression phasereduces the amount of work needed to compress the working fluid 116within the hot cylinder 110. In this way, the Stirling engine usescompression and expansion of the working fluid 116 to convert the heatsupplied at the hot plate 102 into mechanical energy in the form of amoving swash plate 106.

In some embodiments, energy derived from the patient's thermal energycan assist or drive the Stirling engine by supplying at least a portionof the heat delivered to the working fluid 116 through the hot plate102. In some embodiments, the pump system 100 can be incorporated into aportable wound dressing for use in TNP therapy. In at least oneembodiment, a portable wound dressing for use in TNP therapy can includea pump system including a bio-thermic Sterling engine that extendsoperational duration of the portable wound dressing.

In some of the embodiments disclosed herein, the mechanical energy ofthe swash plate 106 can be used to generate a negative pressure for TNPtherapy. In at least one embodiment, the swash plate 106 can generate avacuum pressure by compressing an elastic member such as a spring, abladder, or a foam sponge. In many embodiments, the pump system 100 canbe configured so that the subsequent elastic recovery of the compressedelastic member generates a vacuum pressure, as described below.

In some embodiments, the pump system 100 can include a first bellows124A. In at least one embodiment, the first bellows 124A can be disposedbetween the hot plate 102 and the swash plate 106. In some embodiments,the first bellows 124A can be disposed between the cold plate 104 andthe swash plate 106. In some embodiments, movement of the swash plate106 can compress the first bellows 124A between the swash plate 106 andthe hot plate 110 or between the swash plate 106 and the cold plate 104.In many embodiments, the pump system 100 can include a plurality offirst bellows 124A. In some embodiments, the pump system 100 can have afirst bellows 124A disposed between the swash plate 106 and the coldplate 104 and another first bellows 124A disposed between the swashplate 106 and the hot plate 102.

In some embodiments, the first bellows 124A can be connected to anupstream directional valve 130 that can allow fluid to flow into thefirst bellows 124A while preventing fluid from flowing out of the firstbellows 124A. In some embodiments, the first bellows 124A can be coupledto a downstream directional valve 136, that can allow fluid to flow outof the first bellows 124A while preventing fluid from flowing into thefirst bellows 124A.

In some embodiments, the first bellows 124A can be coupled to a vacuumline 126. In many embodiments, an upstream directional valve 130 cancouple the first bellows 124A to the vacuum line 126. In someembodiments, the upstream directional valve 130 can allow fluid flow inthe direction from the vacuum line 126 into the first bellows 124A andcan restrict fluid flow in the direction from the first bellows 124Ainto the vacuum line 126. In many embodiments, the vacuum line 126 canhave a distal end 132 that can be connected to the first bellows 124Aand a proximal end 134 that can be fluidically coupled to the wound. Insome embodiments, the proximal end 134 of the vacuum line 126 can befluidically coupled to a wound facing surface 222 of a drape 220 thatforms a seal over the wound (see FIG. 2). In at least one embodiment,the vacuum line 126 can fluidically couple to a space formed between thewound and the wound facing surface 222 of the drape 220. In someembodiments, the vacuum line 126 can include a trap 216 (see FIG. 2)that receives wound exudate from the wound and prevents the woundexudate from entering the first bellows 124A. In some embodiments, alayer of the wound dressing such as a layer of gauze can serve as thetrap 216. In some embodiments, a canister can serve as the trap 216. Insome embodiments, the wound exudate can be drawn into the first bellows124A and then pumped out of the first bellows 124A and into an outflowline 142.

In some embodiments, the first bellows 124A can be fluidically coupledto a second bellows 124B by a bellows connecting line 140. In manyembodiments, the bellows connecting line 140 can have directional valves130, 136 that enable fluid to flow from the first bellows 124A to thesecond bellows 124B without allowing the fluid to flow in a retrogradedirection (i.e., from the second bellows 124B to the first bellows124A). In some embodiments, the second bellows 124B can be connected toan outflow line 142. In at least one embodiment, the second bellows 124Bcan be connected to an outflow line 142 having an outlet directionalvalve 137 that prevents fluid from flowing back from the outflow line142 and into the second bellows 124B. In some embodiments, the pumpsystem 100 can have a plurality of first and second bellows 124A, 124B.In at least one embodiment, the pump system 100 can have a first andsecond bellows 124A, 124B disposed between the cold plate 104 and theswash plate 106 and another first and second bellows 124A, 124B disposedbetween the hot plate 104 and the swash plate 106. In some embodiments,the swash plate 106 can generate a vacuum pressure using a plurality offirst and second bellows 124A, 124B mounted onto only the cold plate104, or onto only the hot plate 106, or onto both the cold plate 104 andthe hot plate 106. In many embodiments, the first and second bellows124A, 124B are thermally isolated from the outside environment.

In many embodiments, the heat added to the working fluid 116 can be usedto generate a vacuum pressure. In some embodiments, heat added to theworking fluid 116 within the hot cylinder 110 can cause the workingfluid 116 within the hot cylinder 110 to expand, driving the swash plate106 away from the hot plate 102. In some embodiments, a first bellows124A can be disposed opposite the hot cylinder 110 and between the swashplate 106 and the cold plate 104 so that as the swash plate 106 movesaway from the hot plate 102 the swash plate 106 compresses the firstbellows 124A. In many embodiments, the first bellows 124A can have anoutlet directional valve 137 that allows fluid to flow from the firstbellows 124A into an outflow line 142 as the swash plate 106 compressesthe first bellows 124A. In many embodiments, the first bellows 124A canhave an upstream directional valve 130 that can allow fluid to flow intothe first bellows 124A from a vacuum line 126 as the swash plate 106moves away from the cold plate 104 causing the volume of the firstbellows 124A to expand. In this way, pumping of gas through the firstbellows 124A can be driven in anti-phase to the expansion of the hotcylinder 110. In some embodiments, the first bellows 124A can be elasticand the swash plate 106 can move away from the cold plate 104 as thefirst bellows 124A elastically recovers following compression of thefirst bellows 124A by the swash plate 106. In some embodiments, theswash plate 106 moves away from the cold plate 104 due to momentumimparted to the swash plate 106 during the expansion of the workingfluid within the hot cylinder 110.

In some embodiments, a first bellows 124A can be disposed opposite thecold cylinder 112 and between the swash plate 106 and the hot plate 102so that as the swash plate 106 moves away from the cold plate 104 theswash plate 106 compresses the first bellows 124A. In many embodiments,the first bellows 124A can have an outlet directional valve 137 thatallows fluid to flow from the first bellows 124A into an outflow line142 as the swash plate 106 compresses the first bellows 124A. In manyembodiments, the first bellows 124A can have an upstream directionalvalve 130 that can allow fluid to flow into the first bellows 124A froma vacuum line 126 as the swash plate 106 moves toward the cold plate 104causing the volume of the first bellows 124A to expand. In this way,pumping of gas through the first bellows 124A can be driven inanti-phase to the expansion of the cold cylinder 112. In someembodiments, the first bellows 124A can be elastic and the swash plate106 can move away from the hot plate 102 as the first bellows 124Aelastically recovers following compression of the first bellows 124A bythe swash plate 106. In some embodiments, the swash plate 106 moves awayfrom the hot plate 102 due to momentum imparted to the swash plate 106during the expansion of the working fluid within the hot cylinder 110.

In many embodiments, the pump system 100 can have a regenerator 144. Insome embodiments, the regenerator 144 can be disposed in series with theconnecting line 114. In some embodiments, the working fluid 116 can flowthrough the regenerator 144 as the working fluid 116 passes through theconnecting line 114. In many embodiments, the regenerator 144 can have amaterial that imposes a low impedance on the flow of the working fluid116 when the working fluid 116 flows through the regenerator 144. Inmany embodiments, the regenerator 144 can maintain a temperaturegradient, with the portion of the regenerator 144 closest to the hotcylinder 110 having a higher temperature than the portion of theregenerator 144 closest to the cold cylinder 112. In many embodiments,the regenerator 144 can accept heat from the working fluid 116 as theworking fluid 116 flows from the hot cylinder 110 toward the coldcylinder 112. Similarly, in many embodiments the regenerator 144 cantransfer heat to the working fluid 116 as the working fluid 116 movesfrom the cold cylinder 112 to the hot cylinder 110. In this way, theregenerator 144 may improve efficiency of the pump system 100 byreducing the loss of heat to the surroundings.

The pump systems 100 herein disclosed encompass a variety ofconfigurations of the hot and cold cylinders 110, 112. For example, someembodiments of the pump system 100 can have two hot cylinders 110, twocold cylinders 112 and two connecting lines 114 that are arranged toestablish two independent closed systems that can drive the swash plate106. In at least one embodiment, the pump system 100 can have twoindependent closed systems (as discussed in the previous sentence) withone hot cylinder 110 being 180° circumferentially displaced on the hotplate 102 relative to the other hot cylinder 110. Similarly, someembodiments of the pump system 100 can have one cold cylinder 112 being180° circumferentially displaced on the cold plate 104 relative to theother cold cylinder 112. In at least one embodiment of the pump system100, the hot cylinder 110 can be fluidically connected to a coldcylinder 112 that is 90° circumferentially displaced on the cold plate104 relative to the placement of the hot cylinder 110 on the hot plate102. In some embodiments, the hot cylinder 110 can be fluidicallyconnected to a cold cylinder 112 that is circumferentially displaced onthe cold plate 104 relative to the placement of the hot cylinder 110 onthe hot plate 102 by and angle other than 90°.

In some embodiments, at least a portion of the swash plate 106 can beformed as, or connected to, a traditional piston that moves within thehot and cold cylinders 110, 112. In some embodiments, the hot or coldcylinders 110, 112 can be made of an elastomeric material.

The pump systems 100 herein disclosed also encompass a variety ofconfigurations of the first and second bellows 124A, 124B. In someembodiments, the first and second bellows 124A, 124B can besubstantially linearly aligned with one another, running along adiameter of the hot or cold plates 102, 104. In at least one embodiment,the first bellows 124A can be 90° displaced circumferentially relativeto the second bellows 124B. In many embodiments, the first bellows 124Acan be disposed circumferentially relative to the second bellows 124B byan angle other than 90°. Additional sets of first and second bellows124A, 124B, and additional sets of hot and cold cylinders 110, 112, canbe fitted within a radius of the hot or cold plate 102, 104.

In many embodiments, the pump system 100 can include a set of first andsecond bellows 124A, 124B disposed on the cold plate 104 and a separateset of first and second bellows 124A, 124B disposed on the hot plate102. In at least one embodiment, the set of bellows 124A, 124B disposedon the cold plate 104 can be 90° displaced circumferentially relative tothe set of bellows 124A, 124B disposed on the hot plate 102. In someembodiments, the set of bellows 124A, 124B disposed on the cold plate104 can be displaced circumferentially relative to the set of bellows124A, 124B disposed on the hot plate 102 by an angle other than 90°.Additional sets of first and second bellows 124A, 124B, and additionalsets of hot and cold cylinders 110, 112, can be arranged in series or inparallel. Series arrangements of the bellows or cylinders can generategreater pressure capability, while parallel arrangements of the bellowsor cylinders can allow greater volumetric flow rates of the aspiratedfluid. In some embodiments, the first and second bellows 124A, 124B canhave different diameters or be located on different radii relative tothe hot and cold cylinders 110, 112, enabling an increased pressurecapability of the pump system 100 for a given heat differential.

Additional regenerators 144 can be used as well. In some embodiments,regenerators 144 from separate hot and cold cylinder sets can bethermally, but not fluidically, coupled, allowing heat transfer betweenthe regenerators 144 but not allowing the working fluid 116 within theregenerators 144 to mix. In some embodiments, the regenerators 144 caninclude foam sections, with or without additional materials doping thefoam sections, to alter heat transfer between the regenerator 144 andthe working fluid 116.

In some embodiments, multiple versions of the pump system 100 can bemounted in an array. In some embodiments, certain pump systems 100within the array can be powered by thermal input from the patient whileother pump systems 100 can be powered by external heat sources. In someembodiments, the pump system 100 can include a first set of first andsecond bellows 124A, 124B, or a first set of hot and cold cylinders 110,112, that are fluidically coupled to a second set of bellows orcylinders.

In some embodiments, the hot or cold plates 102, 104 can be made of foamor other flexible material, making the pump system 100 more flexible. Insome embodiments, the flexible hot or cold plates 102, 104 may make thepump system 100 more flexible at the cost of lowering the efficiency ofthe pump system 100. In some embodiments, the hot and cold plates 102,104, or the swash plate 106, can have a shape other than a disc (e.g.,multi-armed cross, star, or ring). In some embodiments, the swash plate106 may include multiple linked plates in place of a single plate. Insome embodiments, one or more materials or layers maybe interposedbetween the swash plate 106 and the hot or cold plate 102, 104. In someembodiments, a dressing may incorporate the pump system 100 and one ormore layers of woven or non-woven, foam, or superabsorber, orcombination thereof.

The pump systems 100 herein disclosed encompass a variety ofconfigurations of the first and second bellows 124A, 124B relative tothe hot and cold cylinders 110, 112. By way of a non-limiting example,in at least one embodiment a first bellows 124A disposed on the hotplate 102 may be axially aligned with a cold cylinder 112 disposed onthe cold plate 104 so that when a portion of the swash plate 106 movesto compress the first bellows 124A the cold cylinder 112 iscontemporaneously expanded by the displacement of that portion of theswash plate 106 away from the cold plate 104. In many embodiments, thehot and cold cylinders 110, 112 may not be axially aligned with thefirst and second bellows 124A, 124B.

In some embodiments, the first and second bellows 124A, 124B can bedisposed on the hot or cold plate 102, 104 at a same radial distance. Insome embodiments, the first and second bellows 124A, 124B can bedisposed on the hot or cold plate 102, 104 at a different radialdistance. In some embodiments, the hot and cold cylinders 110, 112 canbe disposed on the hot or cold plate 102, 104 at a same radial distance.In some embodiments, the hot and cold cylinders 110, 112 can be disposedon the hot or cold plate 102, 104 at a different radial distance. Insome embodiments, the hot and cold cylinders 110, 112 can be arranged onthe hot or cold plate 102, 104 at multiple radii around a center point108, 109 of the hot or cold plate 102, 104. In some embodiments, the hotcylinders 110 can sit on a different Pitch Circle Diameter than the coldcylinders 112. In some embodiments, the first and second bellows 124A,124B can sit on a different Pitch Circle Diameter than the hot or coldcylinders 110, 112.

In some embodiments, the hot plate 102 can have a direct thermalconnection to the patient's skin. In some embodiments, the hot plate 102can include a thermal connection to a separate heat pick-up (not shown)on the patient's skin. In some embodiments, a heating element 146 withor without additional thermal input from the patient's skin can supplyheat to the hot plate 102. In some embodiments, the cold plate 104 canbe passively cooled. In some embodiments, the cold plate 104 can includefins or other features that enhance heat transfer. In at least oneembodiment, the cold plate 104 can be actively cooled by a fan or otherelement that increases heat transfer. In some embodiments, the workingfluid 116 can be a fluid other than air.

In some embodiments, the cold cylinder 112 can be of a different shapeor size compared to the hot cylinder 110. In some embodiments, the firstbellows 124A can be of a different shape or size compared to the secondbellows 124B. In at least one embodiment, the hot and cold cylinders110, 112 can be of the same size and shape. In at least one embodiment,the first and second bellows 124A, 124B can be of the same size andshape. In at least one embodiment, the hot and cold cylinders 110, 112can be the same size and shape as the first and second bellows 124A,124B. In some embodiments, the hot and cold cylinders 110, 112 can be ofa different shape or size compared to the first and second bellows 124A,124B.

In some embodiments, the upstream and downstream directional valves 130,136 can be controlled by a controller to control flow rate. In at leastone embodiment, the upstream or downstream directional valves 130, 136can include a material that changes shape when exposed to eithertemporary or continuous electrical potential (e.g., liquid crystals),allowing a complete close or a complete open of the upstream ordownstream directional valve 130, 136 in additional to normal one-wayfunctionality of the valve. In some embodiments, some or all of theupstream and downstream directional valves 130, 136 can have materialsthat change shape when exposed to pressure, allowing automatic controlof the pressure generated by the pump system 100. In at least oneembodiment, some or all of the upstream or downstream directional valves130, 136 can have a material that swells when exposed to liquid,enabling the pumping system 100 to cease applying a negative pressure tothe wound when the wound exudate begins to enter the first or secondbellows 124A, 124B. In some embodiments, some or all of the upstream ordownstream directional valves 130, 136 can include material that has ahysteresis in its shape with pressure, allowing a cyclic pressure to beapplied to the wound.

In many embodiments, the first and second bellows 124A, 124B can beformed to have a planar profile. By way of a non-limiting example, someembodiments can have first and second bellows 124A, 124B formed asbubbles between two sheets of film or foam, similar to a bubble pack. Insome embodiments, the swash plate 106 can use a shape other than aplate. In many embodiments, the swash plate 106 may have a shape such asa multi-armed cross, a star, or a ring. In some embodiments, the hot andcold plates 102, 104 can be made of foam or other flexible materials,making the pump system 100 more flexible. In some embodiments, the pumpsystem 100 can be made more flexible at the cost of lowering theefficiency of the pump system 100.

In many embodiments, the pump system 100 herein disclosed can make theStirling engine, including the crank mechanism, highly planar and makethe pumping action direct, negating the complexity and energy lossinherent to an intermediate stage. In some embodiments, the use oflarger and flatter the cylinders and bellows can enable greater pressureto be generated. In many embodiments, the planar configuration can makethe pump system 100 suitable for an on-board dressing, particularly whenthe pump system 100 has an array of cylinders and bellows that can scalewith the dressing size.

In many instances, the ratio of swept volumes of the hot and coldcylinders 110, 112 compared to the first and second bellows 124A, 124Bcan give a gearing, which limits the pressure that can be generated witha given heat differential. This means that the pump system 100 can beself-regulating and intrinsically safe, with no control electronics orsystems. Against standard negative pressure would devices, the pumpsystems 100 herein disclosed can be made to run without external energyinput, extending the operation of the device. In some embodiments, thecontinuous operation of the pump system 100 and its ability to be madelarge or arrayed means that the pumping action can be slow, enabling theflow rate of wound exudate to be comparatively low compared to aperiodic running pump. In addition, the lack of mechanical clashing ofcomponents can make the pump system 100 quiet, producing low amounts ofvibration.

In another embodiment of the heat-assisted pump system 200, a thermalacoustic engine (also referred to as a thermoacoustic engine) can beused to assist or to drive the generation of the vacuum pressure that isapplied to the wound. In many embodiments, the pump system 200 can havea thermal acoustic engine that uses heat to generate a sound wave. Thesound wave can then be used to establish a vacuum, as described below.

FIG. 2 depicts an embodiment of a TNP therapy wound dressing having apump system 100 that can include a thermal acoustic engine. In someembodiments, a housing 202 can enclose a working fluid 116. In manyembodiments, a hot heat exchanger 204 can be thermally coupled to ahousing 202. In many embodiments, a cold heat exchanger 206 can bethermally coupled to the housing 202. In some embodiments, the housing202 can be thermally coupled to both a hot heat exchanger 204 and a coldheat exchanger 206. In some embodiments, a stack 210 can be disposedwithin the housing 202. In at least one embodiment, the stack 210 can bedisposed between the hot heat exchanger 202 and the cold heat exchanger206.

In many embodiments, the stack 210 can include a porous material. Insome embodiments, the stack 210 can establish a temperature gradientbetween the hot heat exchanger 204 and the cold heat exchanger 206. Inat least one embodiment, the stack 210 can include a wire mesh. In someembodiments, the stack can be made of a material selected from the groupconsisting of metal, ceramic, or plastic. In many embodiments, the stack210 can allow the working fluid 116 to pass through the stack with thestack imposing a low impedance to the movement of the working fluid 116.In many embodiments, the stack 210 can transfer heat to, or accepts heatfrom, the working fluid 116 as the working fluid 116 passes through thestack 210.

In many embodiments, heat can be added to the working fluid 116 throughthe hot heat exchanger 204 which can be thermally coupled to a heatsource 232. Heat can be withdrawn from the working fluid 116 by the coldheat exchanger 206 which can be thermally coupled to a heat sink 234. Inmany embodiments, at least a portion of the heat added to the workingfluid 116 can come from the patient. In at least one embodiment, the hotheat exchanger 204 can include a thermal pick up that can be coupled tothe patient's skin.

As heat is added to the working fluid 116 at the hot heat exchanger 204,the working fluid 116 can expand, moving through the stack 210 towardthe cold heat exchanger 206. The hotter working fluid 116 can pass itsheat to a neighboring portion of working fluid 116 that is at a lowertemperature. The flow of heat from the hotter working fluid 116 to thecooler working fluid 116 can reduce the temperature of the hotterworking fluid 116, causing the hotter working fluid 116 to contract andmove back toward the hot heat exchanger 204. As the fluid moves backtoward the hot heat exchanger 204, the fluid can receive heat from aneighboring portion of working fluid 116 that is closer to the hot heatexchanger 204. In this way, the thermal energy generated by the heatsource 212 can be transmitted through the working fluid 116 in a“bucket-chain-effect.”

This “bucket-chain” manner of heat transfer within the working fluid 116can cause the working fluid 116 to oscillate or vibrate between the hotheat exchanger 204 and the cold heat exchanger 206. As the working fluid116 oscillates, it can move back and forth within the stack 210. Overtime, the stack 210 can acquire a temperature gradient, with the portionof the stack 210 next to the hot heat exchanger 204 having a highertemperature than the portion of the stack 210 next to the cold heatexchanger 206. The temperature gradient of the stack 210 can enable thestack 210 to draw heat from the working fluid 116 as the working fluid116 moves toward the cold heat exchanger 206 and to add heat to theworking fluid 116 as the working fluid 116 moves toward the hot heatexchanger 204. In this way, the stack 210 can assist the “bucket-chain”manner of heat transfer within the working fluid 116.

The oscillating movement of the working fluid 116 can generate asimilarly oscillating pressure field (i.e., a sound wave) within theworking fluid 116. In many embodiments, the pumping system 200 can usethe mechanical energy of the sound wave to create a vacuum pressure.

In some embodiments, the pump system 200 can have a diaphragm 212. Inmany embodiments, the diaphragm 212 can be enclosed within the housing202. In at least one embodiment, the diaphragm 212 can be disposed atone end of the housing 202, with the diaphragm 212 being closer to thehot heat exchanger 204 than to the cold heat exchanger 206. In at leastone embodiment, the diaphragm 212 can be fitted in a distal end 226 ofthe housing 202. In at least one embodiment, the diaphragm 212 can beflexible and can move in response to the sound wave generated by thethermal acoustic engine.

In some embodiments, the diaphragm 212 can be coupled to an antechamber214. In at least one embodiment, the antechamber 214 can have anupstream directional valve 130 that can allow fluid to flow through thevalve in a direction toward the antechamber 214 but not allow fluid toflow through the valve in a direction away from of the antechamber 214.In some embodiments, the antechamber 214 can have a downstreamdirectional valve 136 that can allow fluid to flow through the valve ina direction away the antechamber 214 but not allow fluid to flow throughthe valve in a direction toward from of the antechamber 214. In at leastone embodiment, the antechamber 214 can have both an upstreamdirectional valve 130 and a downstream directional valve 136.

In some embodiments, the antechamber 214 can be fluidically coupled to avacuum line 126. In at least one embodiment, the vacuum line 126 can befluidically coupled to the antechamber 214 by an upstream directionalvalve 130. In many embodiments, the vacuum line 126 can have a distalend 132 that can couple to the antechamber 214 and a proximal end 134that can be fluidically coupled to wound site. In at least oneembodiment, the proximal end 134 of the vacuum line 126 can couple to amanifold 217 that can transmit to the wound the negative pressuregenerated by the pump system 200. In at least one embodiment, the vacuumline can have a trap 216 that can receive wound exudate from the woundand prevent the wound exudate from entering the antechamber 214. In someembodiments, the antechamber 214 can be coupled to an outflow line 142.In at least one embodiment, the outflow line 142 can be coupled to theantechamber 214 by a downstream directional valve 136.

In many embodiments, the diaphragm 212 can deflect when the sound wavein the working fluid 116 strikes the diaphragm 212. In some embodiments,deflection of the diaphragm 212 in a direction away from the stack 210can cause the pressure within the antechamber 214 to increase, anddeflection of the diaphragm 212 in a direction toward the stack 210 cancause the pressure within the antechamber 214 to decrease. In this way,the diaphragm 212 can transform the sound wave in the working fluid 116to an oscillating pressure field within the antechamber 214.

In some embodiments, the antechamber 214 can have an upstreamdirectional valve 130 that can open when the pressure in the antechamber214 is reduced by movement of the diaphragm 212. In some embodiments,the antechamber 214 can have a downstream directional valve 136 that canclose when the pressure in the antechamber 214 is reduced by movement ofthe diaphragm 212. In at least one embodiment, an upstream directionalvalve 130 that can open when the pressure in the antechamber 214 isreduced by the diaphragm 212 moving in a direction toward the stack 210can couple the antechamber 214 to a vacuum line 126 fluidically coupledto a space disposed between the drape 220 and the wound. In at least oneembodiment, movement of the diaphragm 212 can generate a vacuum pressurethat is applied at the wound. In at least one embodiment, a vacuumpressure generated by the movement of the diaphragm 212 can be strongenough to pull wound exudate out of the wound and into a gauze layer ofa wound dressing or into the vacuum line 126. In some embodiments, thepump system 200 may not have a diaphragm 212, with the sound wavegenerated in the working fluid 116 able to directly cause the upstreamand downstream directional valves 130, 136 to open and close. In atleast one embodiment, the diaphragm 212 can be omitted and air is pulledthrough the vacuum line 126 by the pressure of the sound wave directlyopening and closing the upstream or downstream directional valve 130,136.

In some embodiments, a distal portion 225 of the housing 202 can have aresonator 220 that can tune the vibration of the working fluid 116. Insome embodiments, a distal face 226 of the housing 202 can be a distance230 away from the diaphragm 212. In some embodiments, the distance 230can be a multiple of the wavelength of the sound wave generated by theoscillating working fluid 116. In some embodiments, the distance 230 canbe a full wavelength. In some embodiments, the distance 230 can be ahalf wavelength or a quarter wavelength of the sound wave generated bythe oscillating working fluid 116.

The pump systems 200 disclosed herein encompass a variety ofconfigurations. In some embodiments, the pump system 200 can be part ofthe dressing for a negative pressure wound therapy device. In at leastone embodiment, the pump system 200 can be a separate unit of a negativepressure wound therapy device, the pump system 200 being connected tothe dressing by a conduit. In many embodiments, the pump system 200 canconstitute a portion of a portable wound dressing.

In at least one embodiment, the hot heat exchanger 204 can be coupled tothe patient's skin. In some embodiments, the hot heat exchanger 204 canhave a heat pick-up on the patient's skin. In some embodiments, thermalenergy derived from the patient can supply the heat transferred to theworking fluid 116 by the hot heat exchanger 204. In at least oneembodiment, the hot heat exchanger 204 can be powered by an externalheat source 232 other than the patient. In some embodiments, the hotheat exchanger 204 can be powered by both the patient and an externalheat source 232.

In some embodiments, the cold heat exchanger 206 can be coupled to aheat sink 234. In many embodiments, the cold heat exchanger 206 can be apassive heat exchanger. In some embodiments, the cold heat exchanger 206can have structures, such as fins or convection channels, that aid inthe exchange of heat with the surroundings. In at least one embodiment,the cold heat exchanger 206 can have an active element, such as a fan,to aid in the exchange of heat with the surroundings.

In at least one embodiment, the working fluid 116 can be enclosed withinthe housing 202. In some embodiments, the housing 202 can be open to thesurrounding environment, allowing at least a portion of the workingfluid 116 to communicate with the surrounding environment. In someembodiments, the working fluid 116 can be a fluid other than air.

In some embodiments, the upstream and downstream directional valves 130,136 can be located in positions other than at the end of the housing202. In some embodiments, some, or none, or all, of the upstream anddownstream directional valves 130, 136 can be controlled by a controllerthat controls flow rate of wound exudate out of the wound. In someembodiments, some, or none, or all of the upstream and downstreamdirectional valves 130, 136 can have materials that change when exposedto either temporary or continuous electrical potential, allowingcomplete closed or open of valve in addition to normal one-wayfunctionality. In some embodiments, some or all of the upstream anddownstream directional valves 130, 136 can include materials that changeshape when exposed to pressure, allowing automatic control of thepressure generated by the pump system 100. In some embodiments, some orall of the upstream and downstream directional valves 130, 136 caninclude material that has a hysteresis in its shape in response topressure, allowing the pump system 200 to generate a cyclic pressurethat can be applied to the wound. In some embodiments, the upstream anddownstream directional valves 130, 136 can include material that swellson contact with liquid, allowing the pump system 200 to cease pumpingaction if the dressing becomes full.

In some embodiments, the stack 210 can be doped with additionalmaterials such as foam sections. In some embodiments, correspondinghousings 202 from multiple devices can be arrayed or linked together tooperate in parallel. In some embodiments, a dressing incorporating thepump system 200 can have one or more layer of woven or nonwoven foam, orsuper-absorber, or a combination thereof.

In some embodiments, the hot heat exchanger 204 and cold heat exchanger206 can be inverted relative to the stack 210 (i.e., the cold heatexchanger 206 can be interposed between the stack 210 and the diaphragm212). In some embodiments, the diaphragm 212 can be interposed betweenthe stack 210 and the distal end 226 of the housing 202. In someembodiments, multiple pump systems 200 can be mounted in an array. Insome embodiments, the array of multiple pump systems 200 can be arrangedin series or in parallel. In some embodiments, some pump systems 200 ofthe array can be powered by thermal input from the patient while otherpump systems 200 of the array can be powered by external heat sources.

The pump systems herein disclosed can utilized with a dressing fornegative pressure wound therapy. As shown in FIG. 3A, a pump system 300,which may incorporate or comprise either the pump system 100 or 200previously described, can be located away from the wound site with thenegative pressure generated from the pump system 300 being delivered tothe wound site by a vacuum line 126. In some embodiments, the pumpsystem 300 can be thermally coupled to a portion of the patient's skindistant from the wound site. In some embodiments, the pump system 300can be located at the wound site (see e.g., FIG. 3B). For example, thepump system 300 can be incorporated into the wound dressing 220. In atleast one embodiment, the pump system 300 can be thermally coupled tothe patient and located at the wound site. Further examples of wounddressings that may be utilized in combination with the pump systemsdescribed herein, and further embodiments of negative pressure woundtherapy components that may be incorporated into, or used with, theapparatuses and methods described herein, are found in: PCTInternational Application No. PCT/IB2013/002060, filed Jul. 31, 2013(Attorney Docket No.: SMNPH.228WO2); U.S. patent application Ser. No.14/385136, filed Sep. 12, 2014 (Attorney Docket No.: SMNPH.212NP); U.S.patent application Ser. No. 14/209907, filed Mar. 13, 2014, published asU.S. Pub. 2014/0316359 (Attorney Docket No. SMNPH.246A); U.S. Pat. No.8,905,985, issued Dec. 9, 2014 (Attorney Docket No. SMNPH.194A); U.S.application Ser. No. 14/401356, filed Nov. 14, 2014, published as U.S.Pub. 2015/0100045 (Attorney Docket No.: SMNPH.215NP); and PCTInternational Application No. PCT/GB2011/000625, filed Apr. 21, 2011,published as WO 2011/135285 (Attorney Docket No.: SMNPH.176APC), theentirety of each of which is hereby incorporated by reference, and areprovided as Appendices A-F.

For example, some embodiments of wound dressings that may be utilizedmay comprise an absorbent layer for retaining wound exudate therein,such as the wound dressings available as part of the PICO system fromSmith & Nephew. These negative pressure systems are preferablycanister-less. Other examples include systems that use canisters tocollect wound exudate, such as the RENASYS EZ and RENASYS GO systemsavailable from Smith & Nephew. Such systems may include a wound packingmaterial such as foam or gauze for placement into the wound, one or moreadhesive drapes used to cover the wound and form a seal to skinsurrounding the wound, and a port (such as SOFT PORT, available fromSmith & Nephew) for connecting the drape to a source of negativepressure.

FIGS. 4A-C depict a non-limiting example of a method of use of a wounddressing incorporating a pump system as disclosed herein for treatmentof a wound with negative pressure wound therapy. The skin of the patientnear the wound 400 can be prepared to receive the wound dressing (seee.g., FIG. 4A). The wound dressing can be laid over the wound 400 sothat the drape or backing layer 220 of the wound dressing covers thewound 400 (see e.g., FIG. 4B). The wound dressing can be secured to thepatient's skin by an adhesive tape 402, and/or it may have an adhesivelayer on an underside thereof In some embodiments, the wound dressingcan form a substantially fluid-tight seal that allows a negativepressure generated by the pump system 100, 200 to be applied to thewound 400 through a vacuum line 126.

Although the thermal differential can be low between body heat and theenvironment, operation of the pump system 100 at approximately 0.5%efficiency in some embodiments can be enough to hold a negative pressureof 80 millimeters of mercury. In many embodiments, the pump system 100can operate specifically by generating a defined frequency determined byits geometry, allowing the pump system 100 to be tuned to generate asound wave having a frequency that disturbs the patient least.

The above presents a description of modes contemplated of carrying outthe present invention, and of the manner and process of making and usingit, in such full, clear, concise, and exact terms as to enable anyperson skilled in the art to which it pertains to make and use thisinvention. This invention is, however, susceptible to modifications andalternate constructions from that discussed above which are fullyequivalent. Consequently, it is not the intention to limit thisinvention to the particular embodiments disclosed. On the contrary, theintention is to cover modifications and alternate constructions comingwithin the spirit and scope of the invention as generally expressed bythe following claims, which particularly point out and distinctly claimthe subject matter of this invention.

Features, materials, characteristics, or groups described in conjunctionwith a particular aspect, embodiment, or example are to be understood tobe applicable to any other aspect, embodiment or example describedherein unless incompatible therewith. All of the features disclosed inthis specification (including any accompanying claims, abstract anddrawings), and/or all of the steps of any method or process sodisclosed, may be combined in any combination, except combinations whereat least some of such features and/or steps are mutually exclusive. Theprotection is not restricted to the details of any foregoingembodiments. The protection extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of protection. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms. Furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made. Those skilled in the art willappreciate that in some embodiments, the actual steps taken in theprocesses illustrated and/or disclosed may differ from those shown inthe figures. Depending on the embodiment, certain of the steps describedabove may be removed, others may be added. Furthermore, the features andattributes of the specific embodiments disclosed above may be combinedin different ways to form additional embodiments, all of which fallwithin the scope of the present disclosure.

Although the present disclosure includes certain embodiments, examplesand applications, it will be understood by those skilled in the art thatthe present disclosure extends beyond the specifically disclosedembodiments to other alternative embodiments and/or uses and obviousmodifications and equivalents thereof, including embodiments which donot provide all of the features and advantages set forth herein.Accordingly, the scope of the present disclosure is not intended to belimited by the specific disclosures of preferred embodiments herein, andmay be defined by claims as presented herein or as presented in thefuture.

What is claimed is:
 1. A negative pressure wound therapy system,comprising: a wound dressing configured to form a seal over a wound siteof a patient; a vacuum line fluidically connected to a space disposedbetween the wound dressing and the wound; and a pump system fluidicallyconnected to the vacuum line, the pump system further comprising: ahousing; a hot heat exchanger configured to receive heat from a heatsource thermally connected to the hot heat exchanger; a working fluidthermally coupled to the hot heat exchanger; and a moveable member incontact with the working fluid, the moveable member configured to movewhen the working fluid expands to thereby generate a negative pressurein the vacuum line to draw a fluid from the wound site.
 2. The system ofclaim 1 wherein at least a portion of the heat received by the hot heatexchanger comes from the patient.
 3. The system of claim 1 wherein themoveable member is a swash plate of a Stirling engine.
 4. The system ofclaim 1 wherein the moveable member is a diaphragm of a thermal acousticengine.
 5. The system of claim 1 further comprising a cold heatexchanger configured to deliver heat to a heat sink thermally connectedto the cold heat exchanger.
 6. The system of claim 1 further comprisinga mesh, the mesh being secured to the housing and thermally coupled toat least a portion of the working fluid.
 7. The system of claim 1wherein the wound dressing comprises a drape.
 8. The system of claim 1wherein the wound dressing comprises an absorbent layer for retaining awound exudate.
 9. A pump system for use in negative pressure woundtherapy, the pump system comprising: a pivoting substrate disposedbetween a top substrate and a bottom substrate; a first chamber disposedbetween the pivoting substrate and the bottom substrate; a secondchamber disposed between the pivoting substrate and the top substrate,the second chamber being fluidically connected to the first chamber ontop substrate; and a bellows disposed between the pivoting substrate andthe bottom substrate, the bellows having a directional valve.
 10. Thepump system of claim 9 further comprising a regenerator disposed betweenthe first and second chamber, the regenerator thermally coupled to aworking fluid, the working fluid being at least partially containedwithin the first and second chambers.
 11. A pump system for use innegative pressure wound therapy, the pump system comprising: a hollowbody enclosing a working fluid, the hollow body having a proximal endand a distal end; a diaphragm interposed between the proximal and distalends of the hollow body; an antechamber coupled to the proximal end ofthe hollow body, wherein at least a portion of a wall of the antechamberis defined by the diaphragm; and an inlet directional valve having anopen state and a closed state, the inlet directional valve being in theopen state when a fluid flows into the antechamber and being in theclosed state when the fluid flows out of the antechamber, wherein heatsupplied to the working fluid generates a sound wave within the workingfluid, said sound wave causing the diaphragm to move.